scholarly journals Morphological classification of post-AGB stars

2011 ◽  
Vol 7 (S283) ◽  
pp. 83-86
Author(s):  
Arturo Manchado ◽  
D. Anibal García-Hernández ◽  
Eva Villaver ◽  
Jean Guironnet de Massas
Keyword(s):  
Hubble Space Telescope ◽  
Asymptotic Giant Branch ◽  
Galactic Latitude ◽  
Agb Stars ◽  
Morphological Classification ◽  
Preliminary Results ◽  
Evolutionary Phase ◽  
Complete Study ◽  
Circumstellar Shell ◽  
Pn Stage

AbstractWe present a complete study of the morphology of post-Asymptotic Giant Branch (post-AGB) stars. The post-AGB stage is a very short evolutionary phase between the end of the AGB and the beginning of the Planetary Nebula (PN) stage (between 100 and 10,000 yrs). Post-AGB stars do not show variability and are not hot enough to fully ionize the hydrogen envelope. We have defined the end of the post-AGB phase and the beginning of the PN phase when the star has a temperature of 30000 K. Post-AGB stars have a circumstellar shell that is illuminated by the central stars or partially ionized. However, this circumstellar shell is too small to be resolved by ground-based observations. Thus, we have used the Hubble Space Telescope (HST) database to resolve these shells. 117 post-AGBs were found in this database. Here we present the preliminary results on their morphological classification and the correlation with the galactic latitude. Our preliminary results show that 38% of the sample are stellar-like (S), 31% bipolar (B), 12% multipolar (M) and 19% elliptical (E).

SMA Spectral Line Survey of the Proto-Planetary Nebula CRL 618

2018 ◽  
Vol 14 (S343) ◽  
pp. 483-484
Author(s):  
Nimesh A. Patel ◽  
Carl Gottlieb ◽  
Ken Young ◽  
Tomasz Kaminski ◽  
Michael McCarthy ◽  
...  
Keyword(s):  
Spectral Line ◽  
Planetary Nebula ◽  
Line Emission ◽  
Asymptotic Giant Branch ◽  
60 Ghz ◽  
Agb Stars ◽  
Complex Molecules ◽  
Compact Region ◽  
Line Survey ◽  
Pn Stage

AbstractCarbon-rich Asymptotic Giant Branch (AGB) stars are major sources of gas and dust in the interstellar medium. During the brief (∼1000 yr) period in the evolution from AGB to the Planetary Nebula (PN) stage, the molecular composition evolves from mainly diatomic and small polyatomic species to more complex molecules. Using the Submillimeter Array (SMA), we have carried out a spectral line survey of CRL 618, covering a frequency range of 281.9 to 359.4 GHz. More than 1000 lines were detected in the ∼60 GHz range, most of them assigned to HC3N and c-C3H2, and their isotopologues. About 200 lines are unassigned. Lines of CO, HCO+, and CS show the fast outflow wings, while the majority of line emission arises from a compact region of ∼1” diameter. We have analyzed the lines of HC3N, c-C3H2, CH3CN, and their isotopologues with rotation temperature diagrams.

scholarly journals Dynamics, temperature, chemistry, and dust: Ingredients for a self-consistent AGB wind

2018 ◽  
Vol 14 (S343) ◽  
pp. 129-133
Author(s):  
J. Boulangier ◽  
D. Gobrecht ◽  
L. Decin
Keyword(s):  
Life Time ◽  
Vital Role ◽  
Asymptotic Giant Branch ◽  
Nucleation Theory ◽  
Agb Stars ◽  
Low Mass Stars ◽  
Chemical Enrichment ◽  
Self Consistent ◽  
Evolutionary Phase ◽  
Almost All

AbstractUnderstanding Asymptotic Giant Branch (AGB) stars is important as they play a vital role in the chemical life cycle of galaxies. AGB stars are in a phase of their life time where they have almost ran out of fuel and are losing vast amounts of material to their surroundings, via stellar winds. As this is an evolutionary phase of low mass stars, almost all stars go through this phase making them one of the main contributors to the chemical enrichment of galaxies. It is therefore important to understand what kind of material is being lost by these stars, and how much and how fast. This work summarises the steps we have taken towards developing a self-consistent AGB wind model. We improve on current models by firstly coupling chemical and hydrodynamical evolution, and secondly by upgrading the nucleation theory framework to investigate the creation of TiO2, SiO, MgO, and Al2O3 clusters.

scholarly journals Synthetic P-AGB Evolution

1993 ◽  
Vol 155 ◽  
pp. 473-476 ◽  
Author(s):  
Letizia Stanghellini ◽  
Alvio Renzini
Keyword(s):  
Mass Distribution ◽  
Planetary Nebula ◽  
Asymptotic Giant Branch ◽  
Transition Time ◽  
Mass Relation ◽  
Agb Stars ◽  
Mass Distributions ◽  
Luminosity Functions ◽  
Observational Errors ◽  
Pn Stage

Extensive Montecarlo simulations of Post-Asymptotic Giant Branch (P-AGB) populations have been constructed, exploring the effects of various assumptions on synthetic H-R diagrams, luminosity functions, and inferred mass distributions. Such assumptions include the IMF, the initial mass-final mass relation, the AGB to PN transition time, the duration of the planetary nebula (PN) stage, etc. We have also investigated how the observational errors in luminosity and temperature propagate into the inferred mass distribution of the P-AGB stars.

scholarly journals Molecular processes from the AGB to the PN stage

2011 ◽  
Vol 7 (S283) ◽  
pp. 148-155 ◽  
Author(s):  
D. Anibal García-Hernández
Keyword(s):  
Solid State ◽  
Stellar Evolution ◽  
Organic Molecules ◽  
Asymptotic Giant Branch ◽  
Molecular Processes ◽  
Polycyclic Aromatic ◽  
Circumstellar Shell ◽  
Pn Stage ◽  
Complex Organic ◽  
Late Stages

AbstractMany complex organic molecules and inorganic solid-state compounds have been observed in the circumstellar shell of stars (both C-rich and O-rich) in the transition phase between Asymptotic Giant Branch (AGB) stars and Planetary Nebulae (PNe). This short (~102-104 years) phase of stellar evolution represents a wonderful laboratory for astrochemistry and provides severe constraints on any model of gas-phase and solid-state chemistry. One of the major challenges of present day astrophysics and astrochemistry is to understand the formation pathways of these complex organic molecules and inorganic solid-state compounds (e.g., polycyclic aromatic hydrocarbons, fullerenes, and graphene in the case of a C-rich chemistry and oxides and crystalline silicates in O-rich environments) in space. In this review, I present an observational review of the molecular processes in the late stages of stellar evolution with a special emphasis on the first detections of fullerenes and graphene in PNe.

scholarly journals Modelling dust production in AGB stars

2016 ◽  
Vol 12 (S323) ◽  
pp. 165-168
Author(s):  
Flavia Dell’Agli
Keyword(s):  
Asymptotic Giant Branch ◽  
Dust Particles ◽  
Circumstellar Envelope ◽  
Agb Stars ◽  
Physical Processes ◽  
Dust Production ◽  
Evolutionary Time ◽  
Chemical Surface ◽  
Evolutionary Phase ◽  
The Universe

AbstractAsymptotic giant branch (AGB) stars are among the most important gas and dust polluters of the Universe. The latest AGB evolutionary models take into account dust production in the circumstellar envelope of these stars, starting from a detailed computation of the main physical processes and chemical surface variations occurring in this evolutionary phase. Following the formation and growth of dust particles, they provide the unique possibility of interpreting the AGB population observed in resolved galaxies. The first application was for the Spitzer observations of dusty AGBs in the Magellanic Clouds, characterising carbon-rich and oxygen-rich stars in terms of initial mass, epoch of star formation, evolutionary time on the AGB and dust contribution. The same set of models are able to interpret the CNO surface abundances observed for the PNe of the same galaxies.

scholarly journals Lithium factories in the Galaxy: novae and AGB stars

2009 ◽  
Vol 5 (S268) ◽  
pp. 395-404 ◽  
Author(s):  
Francesca D'Antona ◽  
Paolo Ventura
Keyword(s):  
Globular Clusters ◽  
Second Generation ◽  
State Of The Art ◽  
The State ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Preliminary Results ◽  
The Galaxy

AbstractWe review the state of the art in modelling lithium production, through the Cameron–Fowler mechanism, in two stellar sites: during nova explosions and in the envelopes of massive asymptotic giant branch (AGB) stars. We also show preliminary results concerning the computation of lithium yields from super–AGBs, and suggest that super–AGBs of metallicity close to solar may be the most important galactic lithium producers. Finally, we discuss how lithium abundances may help to understand the modalities of formation of the “second generation” stars in globular clusters.

scholarly journals The Stellar Populations of dE Galaxies in Nearby Groups

2004 ◽  
Vol 21 (4) ◽  
pp. 366-370 ◽  
Author(s):  
G. S. Da Costa
Keyword(s):  
Galaxy Evolution ◽  
Local Group ◽  
Dwarf Galaxy ◽  
Hubble Space Telescope ◽  
Stellar Populations ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Space Telescope

AbstractIn this contribution Gemini-North NIRI J,K-observations are used to investigate the upper-Asymptotic Giant Branch (AGB) intermediate-age population in the M81 Group dwarf elliptical (dE) F8D1. Hubble Space Telescope (HST) ‘snapshot’ V,I-observations are also analysed to investigate the upper-AGB populations in two other M81 Group dEs, DDO 71 and kk077. In all three dEs, significant intermediate-age populations are found. Further, there are sizeable dE-to-dE differences in these populations: F8D1 contains relatively more, and relatively more luminous, upper-AGB stars. These results are compared with existing information for Local Group and Sculptor group dwarfs. It is suggested that ‘environmental harrassment’ plays an important role in governing dwarf galaxy evolution.

Population of AGB stars in the outer Galaxy

2018 ◽  
Vol 14 (S343) ◽  
pp. 508-509
Author(s):  
Ryszard Szczerba ◽  
Ilknur Gezer ◽  
Bosco H. K. Yung ◽  
Marta Sewiło
Keyword(s):  
Galactic Plane ◽  
Initial Study ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Spitzer Space Telescope ◽  
Space Telescope ◽  
Preliminary Results ◽  
Galactic Longitude

AbstractWe present preliminary results of a study aimed at identifying and characterizing the Asymptotic Giant Branch (AGB) stars in the outer Galaxy using the color-color diagram (CCD) that combines the Spitzer Space Telescope and 2MASS photometry: Ks – [8.0] vs. Ks – [24]. Our initial study concentrates on a region in the outer Galactic plane around a galactic longitude l of 105°, where we identified 777 O-rich and 200 C-rich AGB star candidates.

scholarly journals Dust Production around Carbon-Rich Stars: The Role of Metallicity

Universe ◽  
2021 ◽  
Vol 7 (7) ◽  
pp. 233
Author(s):  
Ambra Nanni ◽  
Sergio Cristallo ◽  
Jacco Th. van Loon ◽  
Martin A. T. Groenewegen
Keyword(s):  
Wind Speed ◽  
Galactic Halo ◽  
Magellanic Clouds ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Circumstellar Envelopes ◽  
Chemical Enrichment ◽  
Wide Range ◽  
The Universe

Background: Most of the stars in the Universe will end their evolution by losing their envelope during the thermally pulsing asymptotic giant branch (TP-AGB) phase, enriching the interstellar medium of galaxies with heavy elements, partially condensed into dust grains formed in their extended circumstellar envelopes. Among these stars, carbon-rich TP-AGB stars (C-stars) are particularly relevant for the chemical enrichment of galaxies. We here investigated the role of the metallicity in the dust formation process from a theoretical viewpoint. Methods: We coupled an up-to-date description of dust growth and dust-driven wind, which included the time-averaged effect of shocks, with FRUITY stellar evolutionary tracks. We compared our predictions with observations of C-stars in our Galaxy, in the Magellanic Clouds (LMC and SMC) and in the Galactic Halo, characterised by metallicity between solar and 1/10 of solar. Results: Our models explained the variation of the gas and dust content around C-stars derived from the IRS Spitzer spectra. The wind speed of the C-stars at varying metallicity was well reproduced by our description. We predicted the wind speed at metallicity down to 1/10 of solar in a wide range of mass-loss rates.

Rubidium in Barium Stars

2020 ◽  
Author(s):  
M P Roriz ◽  
M Lugaro ◽  
C B Pereira ◽  
N A Drake ◽  
S Junqueira ◽  
...  
Keyword(s):  
Neutron Source ◽  
Slow Neutron ◽  
Asymptotic Giant Branch ◽  
Neutron Density ◽  
Data Sets ◽  
Agb Stars ◽  
Branching Points ◽  
Theoretical Predictions ◽  
Low Mass ◽  
Chemically Peculiar Stars

Abstract Barium (Ba) stars are chemically peculiar stars that display in their atmospheres the signature of the slow neutron-capture (the s-process) mechanism that occurs in asymptotic giant branch (AGB) stars, a main contributor to the cosmic abundances. The observed chemical peculiarity in these objects is not due to self-enrichment, but to mass transfer between the components of a binary system. The atmospheres of Ba stars are therefore excellent astrophysical laboratories providing strong constraints for the nucleosynthesis of the s-process in AGB stars. In particular, rubidium (Rb) is a key element for the s-process diagnostic because it is sensitive to the neutron density and therefore its abundance can reveal the main neutron source for the s-process in AGB stars. We present Rb abundances for a large sample of 180 Ba stars from high resolution spectra (R = 48000), and we compare the observed [Rb/Zr] ratios with theoretical predictions from AGB s-process nucleosynthesis models. The target Ba stars in this study display [Rb/Zr] <0, showing that Rb was not efficiently produced by the activation of branching points. Model predictions from the Monash and FRUITY data sets of low-mass (≲ 4 M⊙) AGB stars are able to cover the Rb abundances observed in the target Ba stars. These observations indicate that the 13C(α,n)16O reaction is the main neutron source of the s-process in the low-mass AGB companions of the observed Ba stars. We have not found in the present study candidate companion for IR/OH massive AGB stars.

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